In a rotating electric machine having a permanent magnet embedded therein, a rare-earth magnet is occasionally used as the permanent magnet in order to realize high efficiency and size reduction. In particular, an Nd (neodymium) magnet having a considerably high magnetic characteristic is used occasionally. Such an Nd magnet is excellent in magnetic characteristic, but is poor in temperature characteristic because holding power becomes deteriorated as temperature increases (thermal demagnetization). In the Nd magnet, the deterioration of the holding power causes such a problem that the magnet is demagnetized in an irreversible manner because of an external anti-magnetic field. This problem results in deterioration of performance of the rotating electric machine. Hence, a cooling structure for the permanent magnet to be used in the rotating electric machine becomes important in terms of temperature control in the permanent magnet.
Conventionally, there have been proposed various rotating electric machines such as a motor for cooling a magnet and a coil end of a stator by use of cooling oil or the like (refer to, e.g., Japanese Patent Laying-Open No. 2007-20337 (Patent Document 1), Japanese Patent Laying-Open No. 2002-345188 (Patent Document 2) and Japanese Patent Laying-Open No. 2006-25545 (Patent Document 3)). Japanese Patent Laying-Open No. 2007-20337 (Patent Document 1), Japanese Patent Laying-Open No. 2002-345188 (Patent Document 2) and Japanese Patent Laying-Open No. 2006-25545 (Patent Document 3) each disclose such a structure that a cooling oil channel is formed on a core of a rotation shaft and an end plate and cooling oil is supplied via the cooling oil channel to produce a cooling effect.
Patent Document 1: Japanese Patent Laying-Open No. 2007-20337
Patent Document 2: Japanese Patent Laying-Open No. 2002-345188
Patent Document 3: Japanese Patent Laying-Open No. 2006-25545